Revision notes · Chemistry of the atmosphere
Carbon dioxide and methane as greenhouse gases
Greenhouse gases4.9.2.1
Definition: Greenhouse effect is the natural process by which greenhouse gases in the atmosphere absorb heat radiated from the Earth's surface, keeping the planet warm enough to support life.
Greenhouse gases let short wavelength radiation from the Sun reach the Earth's surface, but absorb the longer wavelength radiation the Earth radiates back out, warming the atmosphere.
- •Water vapour, carbon dioxide, and methane are the main greenhouse gases in the atmosphere.
- •Short wavelength radiation from the Sun passes through the atmosphere to the Earth's surface.
- •The Earth radiates this energy back out as longer wavelength radiation, which greenhouse gases absorb and re-radiate, warming the surface and lower atmosphere.
⚠️ Common mistake: Thinking the greenhouse effect itself is a problem — it is a natural, essential process; without it the Earth would be too cold for life. It is the enhanced effect from rising greenhouse gas levels that drives climate change.
🧠 Remember: Short wave in, long wave trapped — that's the greenhouse effect.
Human activities which contribute to an increase in greenhouse gases in the atmosphere4.9.2.2
Human activities are increasing the concentrations of carbon dioxide and methane in the atmosphere, enhancing the greenhouse effect.
| Greenhouse gas | Human activities that increase it |
|---|---|
| Carbon dioxide | Combustion of fossil fuels; deforestation |
| Methane | Livestock farming (digestion and waste); decomposition of rubbish in landfill sites |
- •The rise in atmospheric carbon dioxide over the last 100 years correlates with the increased use of fossil fuels.
- •Based on peer-reviewed evidence, most scientists believe human activity is causing global surface temperatures to rise, resulting in global climate change.
⚠️ Common mistake: Assuming the media always presents the full scientific picture — modelling complex systems like climate change can lead to simplified models, speculation, and opinions based on only part of the evidence.
🧠 Remember: CO₂ ← fossil fuels + deforestation. Methane ← farm animals + landfill.
Global climate change4.9.2.3
Definition: Global climate change is a long-term shift in the Earth's climate and weather patterns, linked to rising average global temperatures.
An increase in average global temperature is a major cause of climate change, with wide-ranging potential effects.
- •Sea level rise, causing flooding and increased coastal erosion.
- •More frequent and severe storms.
- •Changes in the amount, timing, and distribution of rainfall.
- •Temperature and water stress for humans and wildlife.
- •Changes to the food-producing capacity of some regions.
- •Changes to the distribution of wildlife species.
⚠️ Common mistake: Thinking global climate change just means rising temperature — it also covers wider effects such as changing rainfall, storms, and shifts in where species can live.
🧠 Remember: Climate change shifts more than heat: sea, storms, rain, stress, food, species.
The carbon footprint and its reduction4.9.2.4
Definition: Carbon footprint is the total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service, or event.
The carbon footprint can be reduced by a range of actions, though several obstacles make this difficult in practice.
- •Increased use of alternative energy supplies, such as renewables, instead of fossil fuels.
- •Energy conservation — using less energy overall.
- •Carbon capture and storage, where CO₂ is trapped in solvents and stored underground.
- •Carbon taxes and licences that charge for greenhouse gas emissions.
- •Carbon offsetting, for example through tree planting.
- •Carbon neutrality — achieving zero net release of greenhouse gases.
Problems with reducing the carbon footprint include:
- •Scientific disagreement over the causes and consequences of climate change.
- •Lack of public information and education.
- •Lifestyle changes people are unwilling to make, such as giving up cars.
- •Economic considerations, since reduction measures often cost money.
- •Incomplete international co-operation between countries.
⚠️ Common mistake: Thinking carbon neutrality means emitting no carbon dioxide at all — it means net emissions of zero, e.g. balancing emissions with an equivalent amount removed or offset.
🧠 Remember: Footprint down: alternatives, saving, capture, taxes, offsetting, neutrality.
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